The present invention relates to laser transmitters and, more particularly, to laser transmitters that employ an optical compensator assembly to correct for out-of-plumb alignment of the transmitter.
Reference laser beams are generated by a conventional laser transmitters for use in surveying and construction. Most commonly, the reference laser beam is swept back and forth in, or rotated through, a horizontal plane. The reference laser beam is most effective if it is maintained in a precisely horizontal orientation. Typically, this requires that the frame of the transmitter itself be maintained in a precisely vertical or horizontal orientation. Many conventional laser transmitters include optical elements that are arranged to maintain a precise horizontal reference beam by automatically compensating for small out-of-plumb tilting of the transmitter frame.
One common optical compensator is illustrated in U.S. Pat. No. 4,221,483. The optical assembly disclosed therein comprises a positive lens suspended beneath a solid state light source by a light-weight mechanical suspension. The suspension includes a plurality of fine wires which suspend the positive lens so as to permit the lens to shift to a truly vertical position, relative to the light source, under the influence of gravity. The shift to vertical compensates for overall tilt of the transmitter housing. According to a specific aspect of the invention described in the ""483 patent, undesired oscillation or vibration of the lens is reduced by an air or magnetic damping system.
Conventional damping arrangements have achieved limited success, however, and there exists a continuing need for a damping scheme that is more versatile and workable than the variety of conventional damping schemes and that achieves improved damping of vibrations and oscillations in laser transmitters.
This need is met by the present invention wherein a laser transmitter is provided including a specialized compensator assembly damping mechanism. In accordance with one embodiment of the present invention, a laser transmitter is provided comprising a housing, a laser light source, an optical projecting device, a compensator assembly, a compensator assembly suspension, a compensator assembly position detector, a compensator assembly damping mechanism, and an active feedback circuit. The laser light source is coupled to the housing and is operative to generate a beam of laser light. The optical projecting device is positioned to direct the beam of laser light to define a reference beam of light projected out of the housing. The compensator assembly is arranged to provide an optical correction for mis-alignment of the housing relative to a vertical axis. The compensator assembly suspension is arranged to couple the compensator assembly to the housing and defines three degrees of freedom in which the compensator assembly is free to move. The three degrees of freedom include movement along an X-axis orthogonal to the vertical axis, movement along a Y-axis orthogonal to the X-axis and the vertical axis, and rotation through an angle xcex8 in a plane parallel to the X and Y axes. The compensator assembly position detector is arranged to detect a position X1 of the compensator assembly with respect to the X-axis, and a position Y1 of the compensator assembly with respect to the Y-axis.
The compensator assembly damping mechanism includes an X-axis magnetic damping mechanism, a Y-axis magnetic damping mechanism, and a rotational damping mechanism. The rotational damping mechanism is arranged to magnetically damp movement of the compensator assembly through the angle xcex8. The active feedback circuit is arranged to (i) drive the X-axis magnetic damping mechanism so as to increase a damping force generated by the X-axis magnetic damping mechanism as a rate of change of the signal indicative of the position X1, increases, and (ii) drive the Y-axis magnetic damping mechanism so as to increase a damping force generated by the Y-axis magnetic damping mechanism as a rate of change of the signal indicative of the position Y1 increases. The active feedback circuit may additionally be arranged to drive the X-axis magnetic damping mechanism as a function of a time derivative of a signal indicative of the position X1, and drive the Y-axis magnetic damping mechanism as a function of a time derivative of a signal indicative of the position Y1.
The X-axis and Y-axis magnetic damping mechanisms preferably include first and second permanent magnets mechanically coupled to the compensator assembly and first and second coil assemblies positioned proximate the first and second permanent magnets and mechanically coupled to the housing.
The X-axis magnetic damping mechanism is typically displaced from the X-axis by a first displacement angle xcex2x along an arc about a central vertical axis of the compensator assembly and the Y-axis magnetic damping mechanism is typically displaced from the Y-axis by a second displacement angle xcex2y along an arc about the central vertical axis. Accordingly, the active feedback circuit is preferably arranged to compensate for the first displacement angle xcex2x and the second displacement angle xcex2y by executing respective weighted sums of the signals indicative of the position X1 and the position Y1.
The rotational damping mechanism preferably comprises an eddy current damping mechanism including a conductor mechanically coupled to and projecting from the compensator assembly and a magnetic field source mechanically coupled to the housing. The magnetic field source and the conductor are arranged such that the conductor intersects a magnetic field generated by the magnetic field source and is oriented substantially perpendicular to the magnetic field. The conductor preferably comprises a pair of substantially parallel fins, the magnetic field source preferably defines a pair of field zones, and the magnetic field source and the conductor are preferably arranged such that each of the fins intersects one of the pair of field zones.
The beam of laser light generated by the laser light source preferably comprises a primary beam of laser light generated along a first axis. Further, the compensator assembly position detector preferably comprises a position detector light source operative to generate a secondary beam of light along a second axis offset from the first axis and a photodetector. The position detector light source is independent of the laser light source and the compensator assembly position detector is arranged to detect the position X1 and the position Y1 as a function of a position of the secondary beam of light on the photodetector.
In accordance with another embodiment of the present invention, a laser transmitter is provided comprising a housing, a laser light source, an optical projecting device, a compensator assembly, a compensator assembly suspension, a compensator assembly position detector, a compensator assembly damping mechanism, and an active feedback circuit. The compensator assembly damping mechanism includes an X-axis magnetic damping mechanism and a Y-axis magnetic damping mechanism. The X-axis magnetic damping mechanism includes a first permanent magnet mechanically coupled to the compensator assembly, and a first coil assembly positioned proximate the first permanent magnet and mechanically coupled to the housing. The Y-axis magnetic damping mechanism includes a second permanent magnet mechanically coupled to the compensator assembly, and a second coil assembly positioned proximate the second permanent magnet and mechanically coupled to the housing. The active feedback circuit is arranged to (i) drive the X-axis magnetic damping mechanism so as to increase a damping force generated by the X-axis magnetic damping mechanism as a rate of change of the signal indicative of the position X1 increases and (ii) drive the Y-axis magnetic damping mechanism so as to increase a damping force generated by the Y-axis magnetic damping mechanism as a rate of change of the signal indicative of the position Y1 increases.
In accordance with yet another embodiment of the present invention, a laser transmitter is provided comprising a housing, a laser light source, an optical projecting device, a compensator assembly, a compensator assembly suspension, a compensator assembly position detector, a compensator assembly damping mechanism, and an active feedback circuit. The compensator assembly position detector comprises a photodetector and a position detector light source operative to generate a secondary beam of light along a second axis offset from the first axis. The position detector light source is independent of the primary laser light source and the compensator assembly position detector is arranged to detect a position X1 of the compensator assembly with respect to the X-axis and a position Y1 of the compensator assembly with respect to the Y-axis as a function of a position of the secondary beam of light on the photodetector.
Accordingly, it is an object of the present invention to provide an improved laser transmitter that incorporates a damping scheme that is more versatile and workable than the variety of conventional damping schemes and that achieves improved damping of vibrations and oscillations in laser transmitters. Other objects of the present invention will be apparent in light of the description of the invention embodied herein.